黑龙江省新生代火山岩构造环境与地震活动     

陈洪洲  徐亚勤 《东北地震研究》1995,(1)

黑龙江省是中国新生代火山岩广泛分布的地区之一。通过对该省新生代火山岩构造环境的分析指出，本省西部火山岩区为大陆板内裂谷环境，地慢上隆、底辟是裂谷形成火山与地震活动的主要原因，而东部火山岩区火山与地震活动的动力则主要来自西太平洋板块对欧亚板块的俯冲作用。  相似文献   

Stable isotope geochemistry of Alpine ophiolites: a window to ocean-floor hydrothermal alteration and constraints on fluid–rock interaction during high-pressure metamorphism     

I. Cartwright  A. C. Barnicoat 《International Journal of Earth Sciences》1999,88(2):219-235

 The subduction of hydrated oceanic lithosphere potentially transports large volumes of water into the upper mantle; however, despite its potential importance, fluid–rock interaction during high-pressure metamorphism is relatively poorly understood. The stable isotope and major element geochemistry of Pennine ophiolite rocks from Italy and Switzerland that were metamorphosed at high pressures are similar to that of unmetamorphosed ophiolites, suggesting that they interacted with little pervasive fluid during high-pressure metamorphism. Cover sediments also have oxygen isotope ratios within the expected range of their protoliths. In the rocks that escaped late greenschist-facies retrogression, different styles of sub-ocean-floor alteration may be identified using oxygen isotopes, petrology, and major or trace element geochemistry. Within the basalts, zones that have undergone high- and low-temperature sub-ocean-floor alteration as well as relatively unaltered rocks can be distinguished. Serpentinites have δ¹⁸O and δ²H values that suggest that they were formed by hydration on or below the ocean floor. The development of high-pressure metamorphic mineralogies in metagabbros occurred preferentially in zones that underwent sub-ocean-floor alteration and which contained hydrated, fine-grained, reactive assemblages. Given that the transformation of blueschist-facies metabasic rocks to eclogite-facies assemblages involves the breakdown of hydrous minerals (e.g. lawsonite, zoisite, and glaucophane), and will thus liberate considerable volumes of fluids, metamorphic fluid flow must have been strongly channelled. High-pressure (quartz+calcite±omphacite±glaucophane±titanoclinohumite) veins that cut the ophiolite rocks represent one possible channel; however, stable isotope and major element data suggest that they were not formed from large volumes of exotic fluids. Fluids were more likely channelled along faults and shear zones that were active during high-pressure metamorphism. Such strong fluid channelling may cause fluids to migrate toward the accretionary wedge, especially along the slab–mantle interface, which is probably a major shear zone. This may preclude all but a small fraction of the fluids entering the mantle wedge to flux melting. Additionally, because fluids probably interact with relatively small volumes of rock in the channels, they cannot "scavenge" elements from the subducting slab efficiently. Received: 28 January 1999 / Accepted: 2 February 1999  相似文献   

考虑俯冲带潜在震源区的地震危险性算法研究及在中国海域的应用     

李昌珑  温增平 《震灾防御技术》2021,16(1):62-70

本文研究了俯冲带潜在震源区离散化方法及考虑俯冲带高震级地震震源破裂面和震源深度的场点地震动计算方法，推导了俯冲带潜在震源区地震危险性计算公式，并使用中国海域及邻区地震危险性模型进行地震危险性试算。结果表明，本文建立的考虑俯冲带潜在震源区的地震危险性算法能够实现场点地震危险性计算时对俯冲带高震级地震震源破裂面和震源深度的考虑。  相似文献   

两种地幔对流模式下俯冲带的热结构   总被引：10，自引：3，他引：10       下载免费PDF全文

臧绍先  宁杰远 《地球物理学报》1994,37(4):448-455

根据准动力学计算方案，通过采用等效热源和等效热传导系数的方法，用有限元法计算了不同俯冲角度，而俯冲速度为８ｃｍ／ａ、年龄为１００Ｍａ的俯冲带在稳定俯冲状态的热结构．计算结果表明俯冲带在接近６７０ｋｍ间断面的最低温度可达到１１００℃．全地幔对流模式热结构的计算结果表明６７０ｋｍ间断面以下可存在最低温度达１０００℃的低温区，相应于有０．７％-３．０％的Ｐ波低速异常存在．双层地幔对流模式表明，在６７０ｋｍ间断面以上可有与周围地幔相差约４００℃的水平舌状低温区存在，相应于０．５％-１．４％的Ｐ波低速异常．  相似文献   

Multiple ophiolite generation preserved in the northern Philippines and the growth of an island arc complex   总被引：2，自引：0，他引：2  

John Encarnacin 《Tectonophysics》2004,392(1-4):103

Although all oceanic arcs grow through the addition of subduction-generated magmas, the geology of the northern Philippines demonstrates that a major contribution to arc crustal growth can come from repeated, episodic, intra-arc, back-arc, and/or fore-arc oceanic crust generation with subsequent preservation of the basic–ultrabasic units in the arc complex. At least five episodes of oceanic crust generation are represented in the northern Philippines by preserved ophiolitic sequences and recent intra-arc seafloor spreading. Each episode is distinct in age as confirmed by modern dating techniques, with the ages ranging from pre(?)-Jurassic to Quaternary. Although the Philippines is widely regarded as an amalgamation of allochthonous terranes, a review of the available data shows that there is currently no compelling evidence that these ophiolites are of exotic origin and that they have been tectonically accreted to the Philippine arc complex. Rather, the evidence suggests that most—and possibly all—of the ophiolites were generated as back-arc, fore-arc, or intra-arc crust within the Philippine arc complex. Hence, there is a close spatial association of several ophiolitic terranes of diverse ages spanning 150 Myr that formed as part of the arc complex. Such an association may have arisen from episodic generation of oceanic crust during periods of local extension in a suprasubduction zone setting, which has experienced changing and possibly overlapping subduction from the east and west sides (in the current reference frame). Disruption of the ophiolitic basement terranes has been, and continues to be, effected primarily by wrench faulting. This style of arc growth has implications for the paleotectonic interpretation of ancient ophiolite-arc terranes in continents and the petrologic evolution of island arcs.  相似文献   

Tectonic mechanisms associated with P–T paths of regional metamorphism: alternatives to single-cycle thrusting and heating     

John Wakabayashi   《Tectonophysics》2004,392(1-4):193

Metamorphic pressure (P)–temperature (T) paths are commonly used as tools to interpret the tectonic history of orogenic belts, those deformed belts of rocks that record past activity along active plate margins. Many studies and reviews relating P–T path development to tectonics have focused on thrusting–thermal relaxation cycles, with special emphasis on collisional processes. Other studies have assumed that P–T paths resulted from a single tectono-metamorphic event that accounted for the entire burial–exhumation history of the rocks. In many cases, such assumptions may prove invalid.This paper speculates on the relationship of tectonic processes other than thrusting–heating to P–T path development. The processes discussed herein include subduction initiation, triple-junction interactions, initiation and shut off of arc volcanism, subcontinental delamination, and hot spot migration. All of these processes may leave a signature in the metamorphic rock record. Examples are presented from a number of localities, most of which are from the Pacific Rim. Although thrusting–heating cycles have influenced metamorphic evolution in many orogenic belts, the potential impact of other types of tectonic mechanisms should not be overlooked.  相似文献   

Variation of seismic coupling with slab detachment and upper plate structure along the western Hellenic subduction zone     

Mireille Laigle  Maria Sachpazi  Alfred Hirn 《Tectonophysics》2004,391(1-4):85

The western Hellenic subduction zone is characterized by a trenchward velocity of the upper plate. In the Ionian islands segment, complete seismic coupling is achieved, as is predicted by standard plate-tectonic models in which there is no slab pull force because the slab has broken off. The moderate local seismic moment rate relates to a shallow downdip limit for the seismogenic interface. This characteristic may be attributed to the ductility of the lower crust of the upper plate, which allows a décollement between the upper crust of the overriding plate and the subducting plate. Farther south, a deeper downdip limit of the seismogenic interface is indicated by thrust-faulting earthquakes, which persist much deeper in western Crete. A correspondingly larger downdip width of this seismogenic zone is consistent with the suggested larger maximum magnitude of earthquakes here. However, since the seismic moment release rate seems to be moderate in the Peloponnese and western Crete, like in in the Ionian islands, this seismically active interface cannot maintain complete seismic coupling across its larger downdip width. A cause may be the lateral addition of overweight to the part of the slab still attached in Crete, by the free fall of its part that has broken off from the surface further north. This increased slab pull reduces the compressive normal stress across the seismogenic interface and thus causes partial seismic coupling in its shallower part. However, the width of this part may provide an additional area contributing to slip in large earthquakes, which may nucleate deeper on stick-slip parts of the interface. Hints at anomalies in structure and seismicity, which need to be resolved, may relate to the present location of the edge of the tear in the slab.  相似文献   

Where and why do large shallow intraslab earthquakes occur?     

Tetsuzo Seno  Masaki Yoshida 《Physics of the Earth and Planetary Interiors》2004,141(3):183-206

We try to find how often, and in what regions large earthquakes (M≥7.0) occur within the shallow portion (20-60 km depth) of a subducting slab. Searching for events in published individual studies and the Harvard University centroid moment tensor catalogue, we find twenty such events in E. Hokkaido, Kyushu-SW, Japan, S. Mariana, Manila, Sumatra, Vanuatu, N. Chile, C. Peru, El Salvador, Mexico, N. Cascadia and Alaska. Slab stresses revealed from the mechanism solutions of these large intraslab events and nearby smaller events are almost always down-dip tensional. Except for E. Hokkaido, Manila, and Sumatra, the upper plate shows horizontal stress gradient in the arc-perpendicular direction. We infer that shear tractions are operating at the base of the upper plate in this direction to produce the observed gradient and compression in the outer fore-arc, balancing the down-dip tensional stress of the slab. This tectonic situation in the subduction zone might be realized as part of the convection system with some conditions, as shown by previous numerical simulations.  相似文献   

The Misis–Andırın Complex: a Mid-Tertiary melange related to late-stage subduction of the Southern Neotethys in S Turkey     

Alastair Robertson  Ülvi Can Unlügen  Nurdan nan  Kemal Ta li 《Journal of Asian Earth Sciences》2004,22(5):413

The Mid-Tertiary (Mid-Eocene to earliest Miocene) Misis–Andırın Complex documents tectonic-sedimentary processes affecting the northerly, active margin of the South Tethys (Neotethys) in the easternmost Mediterranean region. Each of three orogenic segments, Misis (in the SW), Andırın (central) and Engizek (in the NE) represent parts of an originally continuous active continental margin. A structurally lower Volcanic-Sedimentary Unit includes Late Cretaceous arc-related extrusives and their Lower Tertiary pelagic cover. This unit is interpreted as an Early Tertiary remnant of the Mesozoic South Tethys. The overlying melange unit is dominated by tectonically brecciated blocks (>100 m across) of Mesozoic neritic limestone that were derived from the Tauride carbonate platform to the north, together with accreted ophiolitic material. The melange matrix comprises polymict debris flows, high- to low-density turbidites and minor hemipelagic sediments.The Misis–Andırın Complex is interpreted as an accretionary prism related to the latest stages of northward subduction of the South Tethys and diachronous continental collision of the Tauride (Eurasian) and Arabian (African) plates during Mid-Eocene to earliest Miocene time. Slivers of Upper Cretaceous oceanic crust and its Early Tertiary pelagic cover were accreted, while blocks of Mesozoic platform carbonates slid from the overriding plate. Tectonic mixing and sedimentary recycling took place within a trench. Subduction culminated in large-scale collapse of the overriding (northern) margin and foundering of vast blocks of neritic carbonate into the trench. A possible cause was rapid roll back of dense downgoing Mesozoic oceanic crust, such that the accretionary wedge taper was extended leading to gravity collapse. Melange formation was terminated by underthrusting of the Arabian plate from the south during earliest Miocene time.Collision was diachronous. In the east (Engizek Range and SE Anatolia) collision generated a Lower Miocene flexural basin infilled with turbidites and a flexural bulge to the south. Miocene turbiditic sediments also covered the former accretionary prism. Further west (Misis Range) the easternmost Mediterranean remained in a pre-collisional setting with northward underthrusting (incipient subduction) along the Cyprus arc. The Lower Miocene basins to the north (Misis and Adana) indicate an extensional (to transtensional) setting. The NE–SW linking segment (Andırın) probably originated as a Mesozoic palaeogeographic offset of the Tauride margin. This was reactivated by strike-slip (and transtension) during Later Tertiary diachronous collision. Related to on-going plate convergence the former accretionary wedge (upper plate) was thrust over the Lower Miocene turbiditic basins in Mid–Late Miocene time. The Plio-Quaternary was dominated by left-lateral strike-slip along the East Anatolian transform fault and also along fault strands cutting the Misis–Andırın Complex.  相似文献   

Geochemistry and early Palaeogene SHRIMP zircon ages for island arc granitoids of the Sierra Maestra, southeastern Cuba     

Y. Rojas-Agramonte  F. Neubauer  Y.S. Wan  D.E. Garcia-Delgado 《Chemical Geology》2004,213(4):307-324

The Palaeogene volcanic arc successions of the Sierra Maestra, southeastern Cuba, were intruded by calc-alkaline, low- to medium-K tonalites and trondhjemites during the final stages of subduction and subsequent collision of the Caribbean oceanic plate with the North American continental plate. U-Pb SHRIMP zircon dating of five granitoids yielded ²⁰⁶Pb/²³⁸U emplacement ages between 60.5±2.2 and 48.3±0.5 Ma. The granitoids are the result of subduction-related magmatism and have geochemical characteristics similar to those of magmas from intra-oceanic island-arcs such as the Izu Bonin-Mariana arc and the New Britain island arc, Lesser Antilles. Major and trace element patterns suggest evolution of these rocks from a single magmatic source. Geochemical features characterize these rocks as typical subduction-related granitoids as found worldwide in intra-oceanic arcs, and they probably formed through fractional crystallization of mantle-derived low- to medium-K basalt.  相似文献